Can an Electron Absorb a Photon Without Making a Complete Energy Level Jump?

[triac]

Hi!
Today we discussed atomic physics in our class, and the following question came up: Consider an atom, and consider for example its three lowest energy states. Suppose these correspong to the energies E1,E2 and E3, respectively. Will it be possible for an electron in the lowest energy state to absorb a photon with an energy E, where E2-E1<E<E3-E2? That is to say, is it possible for an electron to absorb a photon whose energy does not correspond to a complete "jumb", and instead make an incomplete "jump" and gain the extra energy as kinetic energy?

I believe it is not possible, but then I recall an event with a silicon disc which appeared non-transparent to visible EM-radiation, but invisible to IR-radiation. The explanation I was told was that the energy in IR radiation didn't suffice to excite any of the electrons in the silicon, but if the energy of the radiation was greater that that of IR it would, and therefore EM-radiation of all frequencies above IR would be abosrbed.

Could somebody please shed some light on this issue?

 

[azntoon]

Yes, it is possible for an electron to absorb a photon whose energy does not correspond to a complete "jump" and gain the extra energy as kinetic energy. This is known as an intersystem crossing, and it is a type of electric dipole transition. Intersystem crossings occur when an electron transitions between two different spin states within the same electronic energy level. For example, if an electron is in its lowest energy state (the ground state) and it absorbs a photon with an energy between E2-E1 and E3-E2, then the electron can make an incomplete jump and gain the extra energy as kinetic energy. The silicon disc example you provided is also an example of an intersystem crossing. In this case, the silicon disc was non-transparent to visible EM radiation, but invisible to IR radiation because it was only able to absorb energy from photons that had an energy greater than that of IR.